The invention relates to a method of estimating motion of a picture portion in an image of a picture signal, comprising determining a number of candidate motion vectors starting from a corresponding number of starting vectors, and selecting a motion vector out of the determined candidate motion vectors.
Such a method is described in U.S. Pat. No. 4,853,775. Therein four starting vectors give rise to four candidate motion vectors, and only that motion vector is selected, out of these four candidate motion vectors, which gives a convergence of the used gradient algorithm with the smallest frame difference. The four starting vectors correspond to motion vectors already estimated for four neighboring pixels in the causal neighborhood of the present pixel.